In a manufacturing process of a semiconductor device, electrical characteristics of the semiconductor device are inspected by a semiconductor testing apparatus at the end of a pre-process or a post-process, so that faults of chips are inspected. In such a semiconductor testing apparatus, a probe apparatus serves as a handling apparatus that interfaces the chips on the semiconductor wafer, and a tester in charge of signal processing when performing an inspection at wafer state or at wafer level. Typically, the probe apparatus includes a movable chuck top (mounting table) configured to mount and support thereon the semiconductor wafer; a probe card having probe needles to be brought into contact with electrodes of each chip, thus allowing the chips to be electrically connected with the tester; and a moving device configured to move the chuck top to align the inspection target chips with respect to the probe needles or to the probe card fixed at a certain position.
As for the semiconductor device for power supply, i.e., a so-called power device such as a power MOSFET or an IGBT, electrodes are formed on both sides of a chip and an electric current is flown in a thickness direction of the chip in order to supply a high current at a high voltage. As for the power MOSFET, for example, a source electrode and a gate electrode are formed on a front surface of a chip, while a drain electrode is formed on a rear surface of the chip. If a constant control voltage is applied to the gate electrode, a high current can be flown between the source electrode and the drain electrode. In case of an IGBT, an emitter electrode and a gate electrode are formed on a front surface of a chip, while a collector electrode is formed on a rear surface of the chip. If a constant control voltage is applied to the gate electrode, a current larger than that of the power MOSFET may be flown between the emitter electrode and the collector electrode.
In the probe apparatus of inspecting electrical characteristics of a power device having electrodes on both sides of a chip at wafer level, in order to electrically connect the tester with the power device or each chip to be inspected, probe needles of a probe card positioned above a semiconductor wafer are brought into contact with electrodes (gate electrode and source electrode/emitter electrode) formed on a front surface of the semiconductor wafer. Meanwhile, as for an electrode (drain electrode/collector electrode) formed on a rear surface of the semiconductor wafer, a top surface of the chuck top is made of a plate-shaped conductor, i.e., a mounting surface conductor, and the electrode formed on the rear surface of the semiconductor wafer and the mounting surface conductor are electrically connected by being brought into direct contact with each other. Further, a measurement line or a transmission line through which a current outputted from the power device is flown may be provided between the mounting surface conductor of the chuck top and a corresponding terminal of the tester.
Generally, in the probe apparatus, the semiconductor wafer needs to be held at a certain position on the chuck top in order to align the semiconductor wafer with the probe card or the probe needles accurately. For the purpose, a vacuum evacuation type attracting device has been used.
Conventionally, as such an attracting device, there are known two types depending on the shape of a vacuum suction hole formed on a mounting surface of the chuck top: a groove type in which a multiple number of annular recesses (suction grooves) are formed concentrically and a hole type in which a multiple number of holes (suction holes) are formed at a regular pitch. Typically, in the groove type attracting device, annular suction grooves each having a groove width of, e.g., about 0.5 mm are concentrically arranged at distance of, e.g., about 15 mm to about 20 mm therebetween in a radial direction. Meanwhile, in the hole type attracting device, suction holes each having a diameter of, e.g., about 0.5 mm are arranged in a lattice shape at a pitch of, e.g., about 10 mm. Accordingly, in case that the mounting table has a size of, e.g., about 8 inches (about 200 mm), the total number of the annular suction grooves in the groove type attracting device may be 6 to 8, and the total number of the suction holes in the hole type attracting device may be in the range from about 300 to about 400. In both of the groove type attracting device and the hole type attracting device, the suction grooves or the suction holes are formed in the mounting surface conductor of the chuck top by mechanical machining such as turning or drilling.
Patent Document 1: Japanese Patent Laid-open Publication No. 2011-089891
Patent Document 2: Japanese Patent Laid-open Publication No. 2012-058225
In the probe apparatus of inspecting the electrical characteristics of the power device having the electrodes on both sides of the substrate at wafer level, the semiconductor wafer is fixed at a certain position on the chuck top by using a vacuum attracting force of the attracting device, and, at the same time, the rear surface of the semiconductor wafer is electrically connected with the mounting surface conductor by being brought into direct contact with the mounting surface conductor. In such a conventional probe apparatus, however, a high electric resistance (wafer contact resistance) on a contact surface between the electrode on the rear surface of the wafer and the mounting surface conductor of the chuck top has been a problem to be solved.
That is, if a constant control voltage is applied to the gate electrode of the power device, the source electrode (or the emitter electrode) and the drain electrode (or the collector electrode) are electrically connected, and the power device is turned on. Here, the power device outputs a current of several hundreds of ampere (A) when a high voltage of, e.g., several thousands of voltage (V) is applied from the tester. This outputted current is introduced to the tester. In inspection of dynamic characteristics, a turn-on time or a turn-off time is measured, whereas in inspection of static characteristics, an on-resistance or the like is measured. Thus, in consideration of measurement accuracy and power loss, it may be desirable that impedance of an outgoing measurement line from the tester to the electrode (the drain electrode or the collector electrode) on the rear surface of the power device is low.
In the conventional probe apparatus, however, since the wafer contact resistance is high, it has been difficult to lower the impedance of the outgoing measurement line. Especially, in the aspect of measurement accuracy, since the wafer contact resistance on the mounting surface of the chuck top is highly non-uniform, reproducibility of measurement in the inspection of electrical characteristics at wafer level has been poor.